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KMID : 0811720090130030241
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Korean Journal of Physiology & Pharmacology
2009 Volume.13 No. 3 p.241 ~ p.249
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Role of T-type Ca2＋ Channels in the Spontaneous Phasic Contraction of Pregnant Rat Uterine Smooth Muscle
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Lee Si-Eun
Ahn Duck-Sun
Lee Young-Ho
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Abstract
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Although extracellular Ca2＋ entry through the voltage-dependent Ca2＋ channels plays an important role in the spontaneous phasic contractions of the pregnant rat myometrium, the role of the T-type Ca2＋ channels has yet to be fully identified. The aim of this study was to investigate the role of the T-type Ca2＋ channel in the spontaneous phasic contractions of the rat myometrium. Spontaneous phasic contractions and [Ca2＋]i were measured simultaneously in the longitudinal strips of female Sprague-Dawley rats late in their pregnancy (on day 18∼20 of gestation: term=22 days). The expression of T-type Ca2＋ channel mRNAs or protein levels was measured. Cumulative addition of low concentrations (＜1 μM) of nifedipine, a L-type Ca2＋ channel blocker, produced a decrease in the amplitude of the spontaneous Ca2＋ transients and contractions with no significant change in frequency. The mRNAs and proteins encoding two subunits (α1G, α1H) of the T-type Ca2＋ channels were expressed in longitudinal muscle layer of rat myometrium. Cumulative addition of mibefradil, NNC 55-0396 or nickel induced a concentration-dependent inhibition of the amplitude and frequency of the spontaneous Ca2＋ transients and contractions. Mibefradil, NNC 55-0396 or nickel also attenuated the slope of rising phase of spontaneous Ca2＋ transients consistent with the reduction of the frequency. It is concluded that T-type Ca2＋ channels are expressed in the pregnant rat myometrium and may play a key role for the regulation of the frequency of spontaneous phasic contractions.
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KEYWORD
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Calcium channels, Nickel, Mibefradil, NNC 55-0396, Spontaneous contractility
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